The present disclosure is directed to an apparatus and method for modulating timbre of a musical instrument stringed with ferromagnetic strings. Specifically, the disclosure is directed to an electromagnetic transducer configured to modulate the timbre of a stringed magnetic instrument by modulating the strength of the magnetic field below the string, without substantially affecting loudness, sensitivity and dynamic range.
Electromagnetic pickups, are used with certain stringed musical instruments, such as electric guitars, form the main character of the sound of the stringed instrument. They affect tonal character, output, and sensitivity by converting string vibrations into electrical signals for subsequent amplification into sound. The pickups typically comprise a magnet system, optionally with one or more permanent magnet elements and one or more magnetic flux conductors made of magnetic or ferromagnetic material to establish a magnetic field within which the strings vibrate, and coils wound on one or more bobbins disposed in the field to generate electrical signals corresponding to flux variations in the field due to the strings' vibrations. These electrical signals are amplified into musical sounds by circuits and equipment that is typical in the art.
The distance from the pickup to the strings determines the strength and sensitivity of the magnetic field acting on the strings, where the output voltage is generated when a string vibrates in the magnetic field. However, a stronger magnetic field may also dampen the vibration of the strings, decreasing sustain and affecting tonal character and/or timbre. Taken to extremes, a very strong magnetic field can cause false harmonics or double notes.
A common complaint regarding the tonality of electric guitars (as well as other electronic stringed instruments) is that the sound produced is too harsh. This harshness is particularly evident at higher pitches. One way of eliminating or reducing the harshness has been to increase the number of turns of wire in the coil or coils (the bobbin). However, doing so also increases the inductance, resistance and capacitance, resulting in a higher impedance of the pickup. This has the undesirable result of reducing the pickup's efficiency (in other words, the ability of the transducer to translate vibration to a discernable electric signal) and dulling the instrument's tonality, especially at the lower pitches.
The sound generated by the pickup apparatus varies in different positions on the stringed instrument both vertically and horizontally along the instrument because of the harmonics created by the vibration. There are variations in tone (the ratio of higher harmonics compared to low), the timbre (the relative strength of different harmonics caused by the position of the nodes of each harmonic) and in the overall level.
Accordingly, it would be beneficial to be able to modulate the timbre of the stringed instrument, whether string-by-string or in total, at a fixed distance of the pickup from the string(s).